$ { \left[\begin{array}{rrr}{2} & {-1} & {-1} \\ {0} & {0} & {3}\end{array}\right]+\left[\begin{array}{rrr}{2} & {0} & {1} \\ {1} & {4} & {-2}\end{array}\right] = {?} } $
Answer: To find the sum of two matrices, add the corresponding items between each matrix. ${\left[\begin{array}{rrr}{2}+{2} & {-1}+{0} & {-1}+{1} \\ {0}+{1} & {0}+{4} & {3}+{-2}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rrr}{4} & {-1} & {0} \\ {1} & {4} & {1}\end{array}\right]}$